HSC PROFILE

2000 Distinguished Scholar is longtime diabetes
detective

Dr. Michael Stern, a research
"detective" who has helped define antecedents of type 2 diabetes, is
the Presidential Distinguished Scholar
for 2000. Professor of medicine and chief of the Division of Clinical
Epidemiology, he spoke at the
2000-2001 Academic Convocation.

Dr. Stern reflected on the many outstanding
colleagues he has worked with over the years. "I am here merely as their
representative," he told the audience. Three of those collaborators, Dr.
Steve Haffner, Dr. Helen Hazuda and Sharon Fowler, joined the Division of
Clinical Epidemiology shortly after it was established in 1976.

Dr. Stern has used epidemiological techniques
to try to discover the reason for the strong tendency toward type 2 diabetes in
Mexican Americans. Few studies had been conducted on the topic by the end of the
1970s. "Now there
are many," he said, "but I believe that ours was one of the first and
probably the longest running, since it is entering its 21st year."

S.A. Heart Study

The Western lifestyle, marked by increased
caloric intake and decreased physical activity, is thought to be driving the
modern epidemic of obesity, diabetes and cardiovascular disease. Dr. Stern and
his colleagues hypothesized that increasing levels of education and affluence in
developed societies such as the United States would result in a slowing or even
a reversal of this epidemic.

Through the San Antonio Heart Study, they
conducted random samples of populations in three types of neighborhoods—low-income,
exclusively Mexican American barrios; middle-income neighborhoods; and
upper-income, suburban neighborhoods. "The idea behind our sampling design
was that the three neighborhood types would reflect increasing levels of
affluence and educational attainment, and, in the case of Mexican Americans,
increasing acculturation to mainstream U.S. society," Dr. Stern said.

The study team surveyed more than 3,300
Mexican Americans and more than 1,850 non-Hispanics. Eight years later, the
scientists recorded outcomes of study participants, indeed finding that the
incidence of type 2 diabetes
in the study groups decreased as socioeconomic status increased. In each of the
neighborhood types, incidence of type 2 diabetes was higher in Mexican Americans
than
in non-Hispanics.

Behavioral changes

Dr. Stern’s team devised behavioral scales
to understand how sociocultural change could lead to a change in disease rate.

The team’s further studies showed that
incidence of type 2 diabetes among Mexicans living in Mexico City is lower than
among San Antonio Mexican Americans of comparable socioeconomic status. The
group theorizes that the Western lifestyle’s poor diet and exercise traits
have not become as ingrained in the Mexico City residents.

Genetic hypothesis

Dr. Stern also discussed the
"Genetic Admixture Hypothesis,"
a scenario to explain why Mexican Americans are more susceptible
to type 2 diabetes than are non-Hispanics.

The hypothesis holds that:

Native Americans for many centuries adapted
to food scarcity, leading to accumulation of diabetes susceptibility genes.

Sudden availability of caloric abundance
has permitted expression of these diabetes susceptibility genes.

Mexican Americans have Native American
ancestry, with an influx of diabetes susceptibility genes from this ancestral
gene pool.

To test the hypothesis, Dr. Stern and his
colleagues, including faculty from the Southwest Foundation for Biomedical
Research, conducted the San Antonio Family Diabetes Study. The scientists began
with 32 diabetic Mexican Americans and enrolled first-, second- and third-degree
relatives of these individuals.

The group examined 417 genetic markers in
diabetic and non-diabetic participants at the start of the study and five years
later. In the diabetics, the scientists found a linkage between genes on human
chromosome 6 and diminished effectiveness of insulin, a protein that controls
blood sugar level in the body. "We have identified a large number of
interesting linkages," Dr. Stern said.

The group has strong evidence for a linkage
of diabetes to a region on chromosome 10. "We recently received funding to
find the actual gene," Dr. Stern said.